Cored ammonium nitrate explosive cartridge



July 17, 1956 J TH ETAL COREID AMMONIUM NITRATE EXPLOSIVE CARTRIDGEFiled Dec. 29, 1950 III/III!IIIIIIIIII'IIIIIII 1 "q I I I I I l I I I lI I I I I I I I I 1. I. a.

INVENTORS JOHN A. RUTH RALPH VINCENT WAKEFIELD BY w ATTORNEY nitedStates CORED AMMONIUM NITRATE EXPLOSIVE CARTRIDGE John A. Ruth, Alton,and Ralph Vincent Wakefield, East Alton, Ill., assignors to OlinMathieson Chemical Coporation, a corporation of Virginia This inventionrelates to an improved blasting cartridge and more particularly toammonium nitrate explosive assemblies of controlled detonation rate andstrength.

It is recognized in the blasting art that the industry requires a familyof blasting explosives which vary in detonation rate and strength over awide range. For instance, in blasting coal an explosive of low strengthand low rate is usually used. In blasting some sandstone and limestone,explosives possessing higher rates and strengths are employed, and insome strip mining operations and hard rock blasting explosivespossessing still higher rates and strengths are required. Pratt in U. S.Patent 1,785,529 attempted to provide such a family of explosives tomeet the above requirements by utilizing a main charge of black blastingpowder with a center core of a nitroglycerine dynamite extendingthroughout the length of the charge. The manufacture of such an assemblyis attended, however, by the disadvantage that a large variety ofdynamites all containing nitroglycerine and varying in explosivecharacteristics must be manufactured and stored as the core material.Furthermore, the numerous well known disadvantages attending blackpowder and nitroglycerine dynamites such as high cost and toxicity withnitroglycerine and low moisture-proofness with black powder and hazardin handling with both nitroglycerine and black powder are obtained withsuch assemblies. Black powder and straight nitroglycerine explosiveshave in large part been supplanted in the industry with less sensitiveexplosives having ammonium nitrate as the principal ingredient. Manyammonium nitrate explosives of this type are relatively insensitive,particularly in small diameter charges, and the inventive efforts in theart have been in large part directed to methods and means for obtainingpropagation of detonation throughout the explosive charge. Favier in U.S. Patent 393,634 attempted to solve this problem by employing a highdensity ammonium nitrate explosive of low sensitivity with a center coreof dynamite or gun cotton. Manufacture and use of such assemblies isattended by the known disadvantages obtained with nitroglycerinedynamites and gun cotton, such as high cost, hazard in handling, and thelike. Lheure in U. S. Patent 905,336 provided a blasting assemblycomposed of ammonium nitrate having a. central bore and a tube oftrinitrotoluene or trinitrobenzine within the bore for the purpose ofobtaining complete detonation of the insentitive ammonium nitrate. Suchan assembly had the disadvantages that no variation in strength could beobtained regardless of the amount of core material in the assembly, andthat the use of the pure ammonium nitrate made it subject to misfiresand failure of propagation from one cartridge to the next in the boreholes. Various other means have been proposed for providing ammoniumnitrate dynamites of various strengths and detonation rates, but, inorder to supply the industry with the required variety in detonationrate and strength, the manufacturer has had to provide dynamites ofwidely varying composition and physical characteristics.

ice

It is therefore an object of this invention to provide an improvedblasting assembly permitting a wide variation in detonation rate andstrength without requiring the manufacture of a series of differentexplosive compositions. Another object of this invention is to provide ablasting assembly of novel composition and construction. Still anotherobject of the invention is to provide a family of blasting explosiveswith a minimum of raw materials at reduced cost. A further object is toprovide an improved ammonium nitrate explosive of the cored-type. Astill further object is to provide a blasting cartridge having a novelcombination of ingredients and improved explosive characteristics.

Further objects will become apparent from the following descriptiontaken in connection with the accompanying drawing in which Figure 1 is alongitudinal sectional elevation of a blasting cartridge illustrating anembodiment of this invention, and

Figure 2 is a cross-sectional view of the cartridge taken at XX ofFigure 1.

The foregoing objects and advantages are accomplished in accordance withthis invention by providing an explosive cartridge in which an ammoniumnitrate explosive forms the base charge and which. is provided with acenter core of trinitrotoluene containing substantially uniformlydistributed therein granular high explosive.

Any explosive having ammonium nitrate as the principal ingredient issuitable and the particular composition of the ammonium nitrateexplosive is not of great importance, it only being necessary that theammonium nitrate explosive be sufficiently sensitive that in thepresence of the core the detonation is propagated throughout theassembly. In any event, the ammonium nitrate explosive should generallyhave a sensitivity no less than that of a standard mixture composed of94.5% ammonium nitrate and 5.5% paraflin with a fineness such that 25%to 40% will pass a 100 mesh screen at a density not in excess of 1.15,all as defined by Kirst and Woodbury in U. S. Patent 1,992,216 and ispreferably in granular form at a density of about 0.8 to 1.2.

The core has a density of not less than about 1.4 and preferably in therange of 1.5 to 1.8, and a weight strength preferably above The core maybe formed by melting the trinitrotoluene, uniformly incorporatingtherein the granular explosive and any other added ingredients, and thencasting the composition in molds of the desired dimensions. Any granularexplosive which has its explosion or ignition temperature above C., sothat it can be incorporated in molten trinitrotoluene without firing,and which has a rate of detonation at a density of 1.5 in excess ofabout 7000 meters per second, but preferably in the range of about 7500to 8000 meters per second may be utilized in accordance with thisinvention, and should be present in an amount within the range of about20% to 80% by weight of the core. Cyclotrimethylene-trinitramine,commonly referred to as cyclonite, has been found particularly suited asthe granular explosive for the purpose. Examples of other suitablegranular explosives are ethylene dinitramine, pentaerythritoltetranitrate, nitrostarch, nitromannite, and the like. The granulationof such high explosive in the core is such that most or more than about50% of it will pass through a standard U. S. 40 mesh sieve andpreferably through a 200 mesh sieve.

It has been found that a family of explosives having detonation ratesvarying within the range from about 4000 meters per second up to about8000 meters per second can be obtained merely by varying the length ofthe center core. The core should have a minimum cross sectional area inthe neighborhood of about M4 square inch and in any event should begreater than 1 square inch. By varying the cross sectional area ordiameter of the core the weight strength of the cartridge may be variedfrom about 60% to about 90%, with a resulting variation in bulk strengthfrom about 40% to about 80%. The term weight strengt as used hereinrefers to the strength as compared with a similar weight of 100%nitroglycerine blasting gelatin. The term bulk strengt as used hereinrefers to the strength as compared with a similar volume of 100%nitroglycerine blasting gelatin. Inasmuch as certain sized charge holesare drilled in blasting operations, bulk strength is of considerableimportance in evaluating an explosive. The core may extend throughoutthe length of the cartridge, in which instance the maximum rate ofdetonation is obtained. When the core length is less than the length ofthe cartridge the rate of detonation is correspondingly reduced.

The ammonium nitrate explosive and the core composition may be soformulated as to be either sensitive or insensitive, as desired, todetonation by means of a standard blasting cap such as the No. 6 or No.8 cap. If both the core and explosive are insensitive to detonation by ablasting cap, the cartridge is detonated by means of a booster chargeplaced at the end of the cartridge. Such a booster charge preferably hasat least the strength of 1000 grams of trinitrotoluene at a density of0.95 for cartridges of about 4 /2 inches in diameter. The composition ofthe core and ammonium nitrate explosive therefore depends in large parton whether or not a cap sensitive cartridge is desired. Having chosenthe desired compositions for core and explosive charge, it is possiblein accordance with this invention to vary the rate of detonation andstrength of the cartridge without having to provide a series of coresand explosives of difierent compositions, etc.

For the purpose of further clarifying the invention, following is aspecific example illustrating a typical embodiment of the invention.

Referring to the drawing, Figures 1 and 2, the ammonium nitrateexplosive 1 was composed of 88.5% ammonium nitrate, 7.5% TNT, 3% coaldust, 0.5% chalk dust, and 0.5% aluminum powder intimately admixed ingranular form at a density of from 0.9 to 1.0 gram per cubic centimeterand having a detonation rate of about 3560 meters per second and aweight strength of about 67%. The core 2 was in cast form and composedof approximately 60% trinitrotoluene and 40% cyclonite. The cyclonitewas in the form of crystals or granules having an average particle sizein the range from about 100 to 200 mesh and was substantially uniformlydistributed throughout the trinitrotoluene in the cast core, the coredensity being in the range from 1.5 to 1.6 grams per cubic centimeterand having a Weight strength of about 98%. The container 3 which wasmade of card board, although other suitable material may be used, wassealed with end caps 4 of similar material and had internal dimensionsof 4 /2 inches in diameter and 20 inches long. The exact construction ofcontainer shown is merely illustrative and may be fashioned in any othersuitable manner, for instance, instead of employing caps 4 to close thecontainer, the rosette-type crimp formed of the end portions of thecontainer, such as is wellknown in the industry, may be used. The corehad a cross sectional area of one square inch and its length wasgoverned by the desired rate of detonation. For

instance, the eii'cct of core length on the rate of detonation is shownin Table I below. The use of granular ammonium nitrate explosivefacilitates loading of the cartridge and if desired spacers 5, formed ofcard board or other combustible material may be utilized to position thecore accurately. Both the ammonium nitrate explosive and core wereinsensitive to a No. 6 cap and the cartridges were detonated by means ofa capsensitive booster composed of 1000 grams of 40% ammonium Table IDetonation Rate, Meters/ Second Gore Length, Inches Table II Core per-Det.

cent by Density Rate Weight Bulk Weight of Cart. (m./ Strength Strengthof Oar- (gr./cc.) sec. (percent) (percent) tridge Cores .25 Square Inchin Cross Section Length (Inches):

Cores .58 Square Inch in Cross Section Cores 1.0 Square Inch in CrossSection Length (Inches)- Cores 1.78 Square Inches in Cross SectionLength (Inches):

Cores 4 Square Inches in Cross Section Length (Inches):

As may be seen from Table II, the strength varies in accordance with theamount of core material present and as the percentage of the corematerial increases the strength likewise increases. With cores of smallcross section there is no great change in strength with increased corelength. With cores of large cross section, the effect of core length onstrength is more pronounced.

The method of assembling the blasting cartridges of this invention isrelatively simple. For example, assuming it is desired to use acylindrical cast core 12 inches in length in a cartridge 20 inches long,the container having its bottom end closed is first filled to a heightof about 4 inches with the granular ammonium nitrate explosive, which ispoured and tamped therein. The core is then inserted in the center ofthe container with its end resting on the ammonium nitrate explosivetherein. Additional ammonium nitrate explosive is then poured and tampedin to fill the remaining space in the container and the top cap is gluedin position to seal the container. With some relatively insensitivecompositions and in some blasting operations where a number ofcartridges are used in a bore hole there may be encountered a tendencyfor some of the cartridges not to detonate. It is therefore within thepurview of this invention to include adjacent the ends of the containera more sensitive explosive such as a wafer of 40% ammoniumnitrate-nitroglycerin dynarnite on the order of /2 inch thickness inorder to provide satisfactory gap sensitivity. Such wafers are utilizedonly when necessary to the particular composition and operation. Thecartridges in the foregoing specific embodiment may as statedhereinbefore be detonated by means of a suitable booster such asgranular trinitrotoluene, or Primacord, or the like. Small amounts ofadditional ingredients having known beneficial effects may likewise beincluded in the core composition, such as ammonium nitrate and sodiumnitrate to supply oxygen and thus make the mixture somewhat moreefficient, other explosives, alunimum powder, and the like. Forinstance, a core composed of 20%75% trinitrotoluene, 20%-75% cyclonite,and %25% aluminum dust is well suited for the purpose.

Various ammonium nitrate explosives in granular form are known in theart and are suitable for use with the core of trinitrotoluene containinggranular high explosive in blasting cartridges of this invention. Forexample, such explosives have been formed by sensitizing am moniumnitrate by intimately admixing therewith powdered aluminum or othermetals, trinitrotoluene, picric acid, ammonium picrate, nitrostarch,pentaerythritol tetranitrate, cyclonite, tetryl, small amounts ofnitroglycerine and the like. The following compositions have been foundwell suited for the purpose and, when utilized with a core ofcomposition similar to that set forth in Example I above and having across section of one square inch and 12 inches long in a 4 /2 inch by 20inch cartridge, give the detonation rates respectively set forth: 91.0%ammonium nitrate, 5.0% trinitrotoluene, 3.0% coal dust, 0.5% aluminumdust, and 0.5% powdered chalk with a detonation rate of 4800meters/second; 86.0% ammonium nitrate, 10.9% trinitrotoluene, 3.0% coaldust, 0.5% aluminum dust, 0.5% powdered chalk with a detonation rate of5460 meters/second; 91.0% ammonium nitrate, 7.5% trinitrotoluene, 0.5%aluminum dust, 0.5% powdered chalk with a detonation rate of 5680meters/second; and 89% ammonium nitrate, 7.5% trinitrotoluene, 3.0% coaldust, 0.5 powdered chalk with a detonation rate of 5080 meters/second,all having a Weight strength of about 67%, and, for example, acomposition containing 60% ammonium nitrate, 20% trinitrotoluene, sodiumnitrate, 5% coal dust, 4.5% aluminum dust and 0.5 chalk dust with adetonation rate of about 4500 meters per second and a weight strength ofabout 56%. Various other suitable compositions having ammonium nitrateas the major constituent and having varying strengths are set forth forexample in the book entitled High Explosive by W. S. Colver published byD. Van Nostrand Company in 1918. For greatest advantage it is preferredthat the ammonium nitrate explosive have a detonation rate less thanabout 4000 meters per second and a weight strength less than about 70%.A preferred ammonium nitrate explosive is one containing from 80% to 95%ammonium nitrate, up to as much as 10% of a sensitizer, such astrinitrotoluene, aluminum dust, or the like, and up to 5% of acarbonaceous material such as coal dust or the like. The invention istherefore applicable to various types of ammonium nitrate explosives andto various core compositions and a novel low cost blasting cartridge isprovided.

While the invention has been described in considerable detail in theforegoing, it will be understood that many variations may be made in theprocedure and compositions without departing from the spirit of theinvention.

Having thus described the invention, what is claimed and desired tosecure by Letters Patent is:

1. An explosive cartridge having a case containing granular ammoniumnitrate having a sensitivity of not less than the sensitivity of anexplosive composition consisting of 94.5 per cent ammonium nitrate and5.5 per cent parafiin and having a granulation whereby from about 25 percent to about 40 per cent will pass through the openings in an 100 meshscreen and compressed to a density of not more than about 1.15, saidgranular ammonium nitrate having a density within the range of about 0.8to about 1.2, and, embedded in said granular ammonium nitrate, a core oftrinitrotoluene having substantially uniformly dispersed thereincrystals of a granular high explosive, said core having a density of notless than about 1.4 and being in contact with the surrounding ammoniumnitrate, said cartridge having a detonation rate of about 4000 to 8000meters per second, a weight strength of about 60 per cent to about 90per cent and a bulk strength of from about 40 per cent to per cent.

2. An explosive cartridge having a case containing granular ammoniumnitrate having a sensitivity of not less than the sensitivity of anexplosive composition consisting of 94.5 per cent ammonium nitrate and5.5 per cent paraffin and having a granulation whereby from about 25 percent to about 40 per cent will pass through the openings in an 100 meshscreen and compressed to a density of not more than about 1.15, saidgranular ammonium nitrate having a density within the range of about 0.8to about 1.2, and, embedded in said granular ammonium nitrate, a core oftrinitrotoluene having substantially uniformly dispersed therein about20 per cent to 80 per cent granular high explosive, said core having adensity of not less than about 1.4 and being in contact with thesurrounding ammonium nitrate, said cartridge having a detonation rate ofabout 4000 to 8000 meters per second, a weight strength of about 60 percent to about per cent and a bulk strength of from about 40 per cent to80 per cent.

3. An explosive cartridge having a case containing granular ammoniumnitrate having a sensitivity of not less than the sensitivity of anexplosive composition consisting of 94.5 per cent ammonium nitrate and5.5 per cent paraffin and having a granulation whereby from about 25 percent to about 40 per cent will pass through the openings in an meshscreen and compressed to a density of not more than about 1.15, saidgranular ammonium nitrate having a density within the range of about 0.8to about 1.2, and, embedded in said granular ammonium nitrate, a core oftrinitrotoluene having substantially uniformly dispersed thereincrystals of a granular high explosive, said core having a density of notless than about 1.4 and being in contact with the surrounding ammoniumnitrate, said cartridge having a detonation rate of about 4000 to 8000meters per second, a weight strength of about 60 per cent to about 90per cent and a bulk strength of from about 40 per cent to 80 per cent,and a cap sensitive booster charge disposed at the end of the cartridge.

References Cited in the file of this patent UNITED STATES PATENTS905,336 Lheure Dec. 1, 1908 2,171,384 Young Aug. 29, 1939 2,231,043Winning Feb. 11, 1941 OTHER REFERENCES Ohart: Elements of Ammunition,page 34 (1946), John Wiley & Sons, N. Y.

1. AN EXPLOSIVE CARTRIDGE HAVING A CASE CONTAINING GRANULAR AMMONIUMNITRATE HAVING A SENSITIVITY OF NOT LESS THAN THE SENSITIVITY OF ANEXPLOSIVE COMPOSITION CONSISTING OF 94.5 PER CENT AMMONIUM NITRATE AND5.5 PER CENT PARAFFIN AND HAVING A GRANULATION WHEREBY FROM ABOUT 25 PERCENT TO ABOUT 40 PER CENT WILL PASS THROUGH THE OPENINGS IN AN 100 MESHSCREEN AND COMPRESSED TO A DENSITY OF NOT MORE THAN ABOUT 1.15, SAIDGRANULAR AMMONIUM NITRATE HAVING A DENSITY WITHIN THE RANGE OF ABOUT 0.8TO ABOUT 1.2, AND, EMBEDDED IN SAID GRANULAR AMMONIUM NITRATE, A CORE OFTRINITROTOLUENE HAVING SUBSTANTIALLY UNIFORMLY DISPERSED THEREINCRYSTALS OF A GRANULAR HIGH EXPLOSIVE, SAID CORE HAVING A DENSITY OF NOTLESS THAN ABOUT 1.4 AND BEING IN CONTACT WITH THE SURROUNDING AMMONIUMNITRATE, SAID CARTRIDGE HAVING A DETONATION RATE OF ABOUT 4000 TO 8000METERS PER SECOND, A WEIGHT STRENGTH OF ABOUT 60 PER CENT TO ABOUT 90PER CENT AND A BULK STRENGTH OF FROM ABOUT 40 PER CENT TO 80 PER CENT.